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Title: Fusion of {sup 48}Ca+{sup 90,96}Zr above and below the Coulomb barrier

Abstract

Fusion-evaporation cross sections were measured in the two systems {sup 48}Ca+{sup 90,96}Zr in an energy range from well below to well above the Coulomb barrier. The sub-barrier fusion of {sup 48}Ca+{sup 90}Zr is reproduced by coupled-channels calculations including the lowest quadrupole and octupole vibrations of {sup 90}Zr, and using a Woods-Saxon potential with a standard diffuseness parameter a = 0.68 fm. However, the fusion cross sections are overestimated above the barrier. The low-energy slope of the excitation function for {sup 48}Ca+{sup 96}Zr is steeper. This implies a larger diffuseness parameter a = 0.85 fm. Fusion cross sections are well fit in the whole energy range, and the effect of the strong octupole vibration in {sup 96}Zr is predominant. The extracted fusion barrier distributions are reasonably well reproduced by calculations for both systems. A comparison with previous data for {sup 40}Ca+{sup 90,96}Zr is made in an attempt to clarify the role of transfer couplings in sub-barrier fusion.

Authors:
; ; ; ; ;  [1]; ; ; ;  [2];  [3];  [4]; ; ; ;  [5];  [6]
  1. INFN, Laboratori Nazionali di Legnaro, I-35020 Legnaro (Padova) (Italy)
  2. INFN and Dipartimento di Fisica, Universita di Padova, I-35131 Padova (Italy)
  3. INFN, Sezione di Napoli, I-80126 Naples (Italy)
  4. Ruder Boskovic Institute, HR-10002 Zagreb (Croatia)
  5. China Institute of Atomic Energy, 102413 Beijing (China)
  6. IReS, UMR7500, IN2P3-CNRS/Universite Louis Pasteur, Boite Postale28, F-67037 Strasbourg Cedex 2 (France)
Publication Date:
OSTI Identifier:
20771353
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. C, Nuclear Physics; Journal Volume: 73; Journal Issue: 3; Other Information: DOI: 10.1103/PhysRevC.73.034606; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; CALCIUM 40; CALCIUM 48; COMPARATIVE EVALUATIONS; COULOMB FIELD; COUPLED CHANNEL THEORY; DISTRIBUTION; EXCITATION FUNCTIONS; HEAVY ION FUSION REACTIONS; OCTUPOLES; QUADRUPOLES; WOODS-SAXON POTENTIAL; ZIRCONIUM 90; ZIRCONIUM 96

Citation Formats

Stefanini, A.M., Behera, B.R., Corradi, L., Fioretto, E., Gadea, A., Wu, Y.W., Scarlassara, F., Beghini, S., Montagnoli, G., Silvestri, R., Trotta, M., Szilner, S., Zhang, H.Q., Liu, Z.H., Ruan, M., Yang, F., and Rowley, N. Fusion of {sup 48}Ca+{sup 90,96}Zr above and below the Coulomb barrier. United States: N. p., 2006. Web. doi:10.1103/PhysRevC.73.034606.
Stefanini, A.M., Behera, B.R., Corradi, L., Fioretto, E., Gadea, A., Wu, Y.W., Scarlassara, F., Beghini, S., Montagnoli, G., Silvestri, R., Trotta, M., Szilner, S., Zhang, H.Q., Liu, Z.H., Ruan, M., Yang, F., & Rowley, N. Fusion of {sup 48}Ca+{sup 90,96}Zr above and below the Coulomb barrier. United States. doi:10.1103/PhysRevC.73.034606.
Stefanini, A.M., Behera, B.R., Corradi, L., Fioretto, E., Gadea, A., Wu, Y.W., Scarlassara, F., Beghini, S., Montagnoli, G., Silvestri, R., Trotta, M., Szilner, S., Zhang, H.Q., Liu, Z.H., Ruan, M., Yang, F., and Rowley, N. Wed . "Fusion of {sup 48}Ca+{sup 90,96}Zr above and below the Coulomb barrier". United States. doi:10.1103/PhysRevC.73.034606.
@article{osti_20771353,
title = {Fusion of {sup 48}Ca+{sup 90,96}Zr above and below the Coulomb barrier},
author = {Stefanini, A.M. and Behera, B.R. and Corradi, L. and Fioretto, E. and Gadea, A. and Wu, Y.W. and Scarlassara, F. and Beghini, S. and Montagnoli, G. and Silvestri, R. and Trotta, M. and Szilner, S. and Zhang, H.Q. and Liu, Z.H. and Ruan, M. and Yang, F. and Rowley, N.},
abstractNote = {Fusion-evaporation cross sections were measured in the two systems {sup 48}Ca+{sup 90,96}Zr in an energy range from well below to well above the Coulomb barrier. The sub-barrier fusion of {sup 48}Ca+{sup 90}Zr is reproduced by coupled-channels calculations including the lowest quadrupole and octupole vibrations of {sup 90}Zr, and using a Woods-Saxon potential with a standard diffuseness parameter a = 0.68 fm. However, the fusion cross sections are overestimated above the barrier. The low-energy slope of the excitation function for {sup 48}Ca+{sup 96}Zr is steeper. This implies a larger diffuseness parameter a = 0.85 fm. Fusion cross sections are well fit in the whole energy range, and the effect of the strong octupole vibration in {sup 96}Zr is predominant. The extracted fusion barrier distributions are reasonably well reproduced by calculations for both systems. A comparison with previous data for {sup 40}Ca+{sup 90,96}Zr is made in an attempt to clarify the role of transfer couplings in sub-barrier fusion.},
doi = {10.1103/PhysRevC.73.034606},
journal = {Physical Review. C, Nuclear Physics},
number = 3,
volume = 73,
place = {United States},
year = {Wed Mar 15 00:00:00 EST 2006},
month = {Wed Mar 15 00:00:00 EST 2006}
}
  • The fusion excitation function of {sup 36}S+{sup 48}Ca has been measured from well above the barrier down to very small cross sections at sub-barrier energies. A steady decrease of the fusion cross sections is observed below the barrier with no pronounced change of slope. The logarithmic derivative saturates and does not reach the value expected for a constant astrophysical S-factor. The S-factor does not show any maximum in the measured energy range. Coupled-channels calculations using a Woods-Saxon potential have been performed.
  • In recent years, a puzzling pattern has been observed in fusion cross sections well below the Coulomb barrier, characterized as a departure from the exponential-like behavior predicted by standard coupled-channels models, known as fusion hindrance. We report on recent fusion measurements performed at the Laboratori Nazionali di Legnaro, in particular the {sup 48}Ca+{sup 48}Ca reaction down to the level of 0.6 {mu}b. Unlike most recent results in this field, we do not observe the typical divergent behavior of the logarithmic derivative; but rather a sort of saturation, albeit at a larger value than predicted with a standard nucleus-nucleus potential.
  • Recent fusion reaction data for the systems {sup 36}S+{sup 48}Ca, {sup 48}Ca+{sup 48}Ca, and {sup 96}Zr+{sup 48}Ca are analyzed within the coupled-channel formalism. The heavy-ion entrance channel potential is calculated employing an improved double-folding prescription. The nonlocal kernel arising from the knock-on exchange component of the effective N-N interaction is localized within the lowest order of the Perey-Saxon approach, including full recoil. The single-particle densities entering the folding integrals are prescribed according to the density matrix expansion method. The investigation is more elaborated because each case is tested with four different types of N-N effective forces: The two standard parametrizationsmore » of the density-independent M3Y force (Reid and Paris) and two parametrizations of the density-dependent Gogny force (D1S and D1N). A consistent description of all three reactions is achieved by keeping fixed the nuclear structure input for {sup 48}Ca. The inclusion of 2{sup +} and 3{sup -} phonon states in the coupled-channel calculation, within an energy excitation window identical for all three reactions explains better the hindrance in extreme sub-barrier fusion cross sections. The interactions providing the best fit to the data are not pointing to a possible maximum in the astrophysical S factor, thereby confirming the conclusion reached by the Legnaro group for these cases.« less